Have you seen the latest in vinyl fencing? It looks like masonry. Or, install the brick pillars and use masonry screws to hold strips of treated wood between them, to create a surface to which you can easily attach wood or vinyl panels between the pillars.

I fell in love with brick walled gardens in England and always wanted to wall off a small section of ours to create my own, but Illinois farms aren't English estates, so it never happened. I feel your pain at being unable to fulfill your own desire for one.